1. Field of the Invention
This invention relates to a laser apparatus. The present invention also relates to a gyro utilizing a laser apparatus.
2. Related Background Art
Known gyros for detecting the angular velocity of a moving object include mechanical gyros comprising a rotor or an oscillator as well as optical gyros. Particularly, optical gyros are bringing forth technological innovations in the field of gyro technologies due to their remarkable advantages including that they can start to operate instantaneously and show a broad dynamic range. Various optical gyros are known to date including ring laser type gyros, optical fiber gyros and passive type gyros. Of these, the ring laser type gyro that utilizes a gas laser was the earliest to be developed and gyros of this type are popularly used in airplanes at present. In recent years, small and highly sophisticated ring laser type gyros that are formed on a semiconductor substrate have been proposed. See, inter alia, Japanese Patent Application Laid-Open No. 5-288556.
According to the above patent publication, a ring-shaped gain waveguide 5711 having a pn-junction is formed on a semiconductor substrate 5710 and carriers are injected into the gain waveguide 5711 from an electrode 5722, as shown in FIG. 55 of the accompanying drawings, in order to generate a laser oscillation. Then, the laser beams that are propagating through the gain waveguide 5711 clockwise and counterclockwise are partly taken out and caused to interfere with each other in an photo-absorption region 5717. Then, the interfering beams are taken out through another electrode 5723 as a photoelectric current to see the intensity of interference. In FIG. 55, reference numerals 5715 and 5716 respectively denote intensity of interference. In FIG. 55, reference numerals 5715 and 5716 respectively denotes beams propagating clockwise and counterclockwise and reference numerals 5718 and 5719 denote optical outputs, while reference numeral 5712 denotes a reflection plane and reference numerals 5713 and 5714 denote optical output surfaces.
Japanese Patent Application Laid-Open No. 57-43846 (U.S. Pat. No. 4,431,308) describes a gyro that comprises a semiconductor laser element and is adapted not to take the beams of the semiconductor laser element outside thereof, but to utilize the change in the terminal voltage of the element produced by the rotary motion thereof. Referring to FIG. 56 of the accompanying drawings, semiconductor laser element 5792 has upper and lower electrodes (5790 and 5791). In FIG. 56, reference numeral 5793 denotes a DC blocking capacitor and reference numeral 5794 denotes an output terminal, while reference numeral 5795 denotes a resistor. As seen from FIG. 56, the semiconductor laser element of the ring laser device is connected to a drive power source 5796 and the frequency difference (beat frequency) between the frequency of the beam propagating clockwise and that of the beam propagating counterclockwise that is produced when the device shows a certain angular velocity is detected as a change in the terminal voltage of the laser element.
Japanese Patent Application Laid-Open No. 4-174317 also describes a technology of detecting the change in the terminal voltage of a laser element produced as a result of a rotary motion thereof.
However, any of the technologies as described in the above patent documents cannot detect the sense of rotation of an object. This is because an equal beat frequency is detected regardless of the sense of rotation so long as the object is rotating at a same angular velocity.
Thus, known ring laser type gyros are not adapted to detect the sense of rotation of themselves and therefore the sense of rotation has to be determined by applying a dither (micro-oscillation) and determining the correlation of the dither and the obtained signal.
Additionally, in known ring laser type gyros, the oscillation frequencies are separated from each other as the gyro rotates. The difference of the oscillation frequencies is very small small when the rate of revolution is low and then there arises a locking-in phenomenon where the oscillation frequencies are locked to one of the modes of oscillation. This locking-in phenomenon observable in known ring laser type gyros can be avoided by applying a dither.
Thus, it is an object of the present invention to provide a gyro that can detect the sense of rotation of an object.
Another object of the present invention is to provide a ring resonator type gyro that can detect the sense of rotation without using a mechanical device such as a dither generator.
According to the invention, the above objects are achieved by providing a gyro comprising:
a first laser adapted to generate a first laser beam propagating in one direction as a main mode of operation; and
a second laser adapted to generate a second laser beam propagating in one direction as a main mode of operation;
so as to take an electric signal out of at least one of the first laser and the second laser;
the first laser beam and the second laser beam having different respective oscillation frequencies and interfering with each other.
Preferably, in a gyro according to the invention as set forth above, the first laser has a first optical waveguide and the second laser has a second optical waveguide with at least a part of the first optical waveguide and at least a part of the second optical waveguide being arranged in proximity.
Preferably, in a gyro according to the invention as set forth above, the first laser has a first optical waveguide, the second laser has a second optical waveguide, and a third optical waveguide is provided and optically coupled to at least a part of the first and second optical waveguides.
Preferably, in a gyro according to the invention as set forth above, the first laser has a first optical waveguide and the second laser has a second optical waveguide, and the gyro further comprises a third optical waveguide connected to at least a part of the first and second optical waveguides.
Preferably, in a gyro according to the invention as set forth above, the first laser has a first optical waveguide and the second laser has a second optical waveguide with the first optical waveguide and the second optical waveguide being at least partly shared.
Preferably, in a gyro according to the invention as set forth above, the first laser beam and the second laser beam propagate in opposite directions.
Preferably, in a gyro according to the invention as set forth above, the first laser beam and the second laser beam propagate in the same direction.
Preferably, in a gyro according to the invention as set forth above, the first laser has a first optical waveguide and the second laser has a second optical waveguide with both the first optical waveguide and the second optical waveguide having an asymmetrically tapered region.
Preferably, in a gyro according to the invention as set forth above, the tapered region includes a first tapered section and a second tapered section and either the first tapered section or the second tapered section forms an angle of 90xc2x0 with a portion of the optical waveguide having a constant width.
Preferably, in a gyro according to the invention as set forth above, the first laser has a first optical waveguide and the second laser has a second optical waveguide, the first and second optical waveguides having respective optical elements adapted to differentiate the transmission loss of the laser beam propagating in one direction from the transmission loss of the laser beam propagating in the opposite direction.
Preferably, in a gyro according to the invention as set forth above, the first laser is driven with a constant voltage while the second laser is driven with a constant current.
According to the invention, there is also provided a gyro comprising:
a first laser adapted to generate a first laser beam propagating in one direction as a main mode of operation; and
a second laser adapted to generate a second laser beam propagating in one direction as a main mode of operation;
the first laser having a first optical waveguide, the second laser having a second optical waveguide, a third optical waveguide being provided and optically coupled to at least a part of the first and second optical waveguides.
According to the invention, there is also provided a gyro comprising:
a first laser adapted to generate a first laser beam propagating in one direction as a main mode of operation; and
a second laser adapted to generate a second laser beam propagating in one direction as a main mode of operation;
the first laser having a first optical waveguide, the second laser having a second optical waveguide with a third optical waveguide being provided and connected to at least a part of the first and second optical waveguides.
According to the invention, there is also provided a gyro comprising:
a first laser adapted to generate a first laser beam propagating in one direction as a main mode of operation; and
a second laser adapted to generate a second laser beam propagating in one direction as a main mode of operation;
the first laser having a first optical waveguide, the second laser having a second optical waveguide, and the first optical waveguide and the second optical waveguide are at least partly shared.
According to the invention, there is also provided a gyro comprising:
a first laser adapted to generate a first laser beam propagating in one direction as a main mode of operation;
a second laser adapted to generate a second laser beam propagating in one direction as a main mode of operation; and
a beat signal detection means;
the first laser beam and the second laser beam having different respective oscillation frequencies and interfering with each other.
Preferably, in a gyro according to the invention as set forth above, the beat signal detection means detects the voltage signal being applied to the first or second laser, the current signal flowing through the first or second laser, or the impedance signal of the first or second laser.
Preferably, in a gyro according to the invention as set forth above, the first or second laser is provided with an electric terminal for taking out the beat signal.
Preferably, in a gyro according to the invention as set forth above, the beat signal detection means includes a photodetector arranged outside the first and second lasers.
According to the invention, there is also provided a gyro comprising:
a first laser adapted to generate a first laser beam propagating in one direction as a main mode of operation;
a second laser adapted to generate a second laser beam propagating in one direction as a main mode of operation; and
a photodetector for receiving the first and second laser beams;
the first laser beam and the second laser beam having different respective oscillation frequencies and interfering with each other.
According to the invention, there is also provided a gyro comprising:
a first laser adapted to generate a first laser beam propagating in one direction as a main mode of operation; and
a second laser adapted to generate a second laser beam propagating in one direction as a main mode of operation;
the first laser beam and the second laser beam having different respective oscillation frequencies and interfering with each other.